Conventionally, to improve yield of core materials used for production of laminated cores, a method of producing wound cores has been known which includes punching out plural segment core sheets connected in a band shape from a magnetic steel strip, and winding and laminating the band of core sheets. Production of the wound cores does not employ blanking of annular shaped core sheets from a core material. In particular, as disclosed in Patent Documents 1 to 3, for example, arc-shaped segment core sheets connected by connecting portions are punched out of a core material by means of die devices. The segment core sheets each have a predetermined number of slots. Then, the connecting portions which are located in the outer peripheral areas are bent and the side edges of the adjacent segment core sheets are fitted to each other to wind and laminate the plural continuous core sheets in a spiral form.
In the conventional art disclosed in the Patent Documents 1 to 3, however, at the time of bending the connecting portions to position the plural segment core sheets in an annular form, expanded parts are formed in the connecting portions in the thickness direction thereof. The expanded parts create gaps between the laminated segment core sheets, causing the obtained laminated core to have uneven thickness. The gaps reduce efficiency of the motor or cause vibration therein to negatively affect the motor quality.
FIGS. 6(A), 6(B) and 7(A), 7(B) illustrate examples of techniques for eliminating the gaps created by the expanded parts.
In the technique of FIG. 6(A), sections of connecting portions 81 to be subject to compression stress are coined (pressed) in the step of punching out plural segment core sheets 80 in order to reduce the increase in thickness (material thickness) caused by bending of the connecting portions 81. The technique allows the bent connecting portions 81 to have thickness equal to or less than that before the coining, even if the thickness is increased.
In the technique of FIG. 6(B), after bending of connecting portions 86 located between segment core sheets 85, sections of the connecting portions 86 increased in thickness by the bending are flattened in the thickness direction thereof.
In the technique of FIG. 7(A), through-holes 92 are formed in segment core sheets 90 so that sections of the connecting portions 91 increased in thickness by bending of the connecting portions 91 can escape into the through-holes 92 in the segment core sheets 90 laminated above and below the connecting portions 91.
In the technique of FIG. 7(B), cutouts 97 are formed in segment core sheets 95 so that sections of the connecting portions 96 increased in thickness by bending of the connecting portions 96 can escape into the cutouts 97 in the segment core sheets 95 laminated above and below the connecting portions 96.    [Patent Document 1]    Japanese Unexamined Patent Application Publication No. 01-264548    [Patent Document 2]    Japanese Unexamined Patent Application Publication No. 08-196061    [Patent Document 3]    Japanese Translation of PCT International Application No. 2004-505595